The invention relates to an infinitely variable traction roller transmission in which motion is transmitted from a toric disc mounted on an input shaft to a toric disc mounted on an output shaft by traction rollers which are pivotally supported between the toric discs and disposed in engagement with variable diameter circles of the toric discs.
In such transmissions, the traction rollers are pivotally supported on support trunnions which are usually axially movable to initiate changes of the transmission ratio. Such transmission ratio change is possible in a wide range between the two roller pivot end positions in which the traction rollers engage the smallest circle area of one and the largest circle area of the other of the input and output toric discs and vice versa. The pivot end positions of the traction rollers are determined by stop members associated with the traction roller support trunnions. However, even in the pivot end position, there may be forces applied urging the traction rollers to further transmission change or the rollers may not be in perfect position which results in spin of the rollers accompanied by losses and wear of the traction surfaces.